1. Technical Field
The invention relates to an electronic device. More specifically, the invention relates to a semiconductor memory device and a method of operating the same.
2. Related Art
Semiconductor memory devices are memory devices implemented using a semiconductor such as silicon (Si), germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), or the like. The semiconductor memory devices are largely classified as volatile memory devices and non-volatile memory devices.
A volatile memory device is a memory device in which stored data disappears when power supply is cut off. Volatile memory devices include a static random access memory (SRAM), a dynamic RAM (DRAM), a synchronous DRAM (SDRAM), and the like. A non-volatile memory device is a memory device in which the stored data is maintained even when the power supply is cut off. Non-volatile memory devices include a read-only memory (ROM), a programmable ROM (PROM), an erasable programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), or the like. Flash memories are largely classified as a NOR type or a NAND type.
The flash memories may be classified as a two-dimensional semiconductor device in which a string is horizontally formed on a semiconductor substrate and a three-dimensional semiconductor device having a structure in which a string is vertically formed on the semiconductor substrate or a plurality of strings are stacked on the semiconductor substrate.